Unroot and install the original recovery

Hello
I have a Nexsus 5 D820(E)

i need to unroot and install the original recovery

I followed the instruction here
http://forum.xda-developers.com/show...64&postcount=1

Error

Quote:

C:\Windows\system32>fastboot flash bootloader C:\hammerhead-lmy48b\bootloader.img target reported max download size of 1073741824 bytes sending 'bootloader' (3119 KB)... FAILED (data transfer failure (Unknown error)) finished. total time: 5.250s

i need help

ty :)